def visit_When(self, node):
cond = tuple([self.visit(c)
for c in node.condition]) if node.condition else None
statement = self.visit(node.statement)
return vast.Case(cond, statement)
def lower_fsm(fsm: FSM):
assert fsm.start_state == 0, "Starting state is not 0"
zero = vast.IntConst(0)
all_registers = [
Register("a", 8),
Register("b", 8),
Register("tmp", 8),
Register("_cond", 1),
]
register_defs = [
vast.Reg(
reg.name,
vast.Width(vast.IntConst(reg.width -
1), zero) if reg.width - 1 != 0 else None)
for reg in all_registers
]
ports = vast.Portlist([
vast.Ioport(vast.Input('clk')),
# XXX(rachit): AST can't represent `output reg done`
# so assign to a local register and use a wire.
vast.Ioport(vast.Output('done')),
])
done_state = max(fsm.actions.keys()) + 1
done_reg = vast.Reg('done_out')
hook_up_done = vast.Assign(
vast.Lvalue(vast.Identifier('done')),
vast.Rvalue(vast.Identifier('done_out')),
)
# Register to store the FSM state.
fsm_reg_size = int(math.ceil(math.log2(done_state))) + 1
fsm_reg = vast.Reg(name="fsm_reg",
width=vast.Width(vast.IntConst(fsm_reg_size - 1), zero))
# Define all the registers.
reg_decl = register_defs + [fsm_reg]
# Define the initial process
inits = vast.Initial(
vast.Block([
vast.BlockingSubstitution(
vast.Lvalue(vast.Identifier(reg.name)),
vast.Rvalue(vast.IntConst(0)),
) for reg in reg_decl
]))
# Default case, assigns to the done register.
done = vast.IntConst(done_state)
default_case = vast.Case(cond=None,
statement=vast.Block([
vast.NonblockingSubstitution(
vast.Lvalue(vast.Identifier(reg.name)),
vast.Rvalue(vast.Identifier(reg.name)),
) for reg in reg_decl
] + [
vast.NonblockingSubstitution(
vast.Lvalue(vast.Identifier('done_out')),
vast.Rvalue(vast.IntConst(1)))
]))
# Generate Case conditions for each transition.
cases = [
vast.Case([vast.IntConst(cond_val)],
lower_action(fsm_reg, done, action))
for (cond_val, action) in fsm.actions.items()
]
case_statement = vast.CaseStatement(comp=vast.Identifier(fsm_reg.name),
caselist=cases + [default_case])
always_ff = vast.Always(
vast.SensList([vast.Sens(vast.Identifier('clk'), 'posedge')]),
vast.Block([case_statement]))
return vast.ModuleDef(name="main",
paramlist=vast.Paramlist([]),
portlist=ports,
items=reg_decl +
[done_reg, hook_up_done, inits, always_ff])